JP2002309396A - Plate-making plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plate-making plating method by which a uniform coating film of an electrodeposition photoresist is obtained and high quality plating is applied. SOLUTION: In the plate-making plating method which is performed by forming the resist film of the electrodeposition photoresist on the whole surface of a material to be plated, pattern exposing and successively developing, forming an opening part corresponding to a part to be plated on the resist film and stripping the resist film after the plating, the resist film of the electrodeposition photoresist is formed by using an electrodeposition vessel 10 in which an anode 11 is separated from a cathode 12 by a partition 15 passing an electrolyte, but not passing a resist aggregated material. Because the aggregated material of the electrodeposition photoresist is generated in the anode 11 side and does not exist in the cathode 12 side by the partition 15, the abnormality in the resist film, of the defects such as the remaining of the resist, uneven plating, or the chipping of plating is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of plate making and plating, and more particularly to a plate making and plating method suitable for applying a plating required for wire bonding to a lead frame for forming a semiconductor package. Things.

[0002]

2. Description of the Related Art In general, a so-called metal lead frame is used as the most typical skeleton of a resin package among semiconductor packages. The lead frame is a conductive material for electrically connecting the semiconductor element to the outside. Usually, a metal plate having a thickness of 0.1 to 0.25 mm is used. It also plays the role of the mediator and diffuses the heat generated in the semiconductor device. As a material of the lead frame, an iron alloy type and a copper alloy type are mainly used, and the tip of the inner lead is plated with silver or gold for connection in order to perform wire bonding.

In such a semiconductor package, if metal other than the base material is present in the package line, dentite (leaf streak) is generated, leading to migration. Therefore,
QFN (Quad Flat Non-Leaded Package) shown in Fig. 1
As shown in the figure, the back-mounted package in which external terminals are built into the package itself has short leads. Must be performed with precision.

In the QFN shown in FIG. 1, a die pad 2 is supported by suspension leads of a lead frame 1 at four corners, and a semiconductor element 4 is mounted on the die pad 2 via a die bond paste layer 3. The electrode on the upper surface of the element 4 and the lead 5 of the lead frame 1
, And an area surrounding the semiconductor element 4 including the wire 6 is molded with a sealing resin 7 with a part of the lead 5 exposed.

When plating the wire bonding area of the lead frame as described above, the conventional jig plating method has a limit of ± 0.15 mm due to the accuracy of the jig itself and the positioning accuracy of the jig and the lead frame. Further, it is not possible to prevent the plating from adhering to the side surface, and therefore, it cannot be applied to a lead frame for a back-mount package such as the above-mentioned QFN.

For this reason, a plate making plating method has been adopted as a means for plating a wire bonding area of a lead frame. That is, a photoresist is applied to the entire lead frame, the photomask and the lead frame are aligned using the jig hole as an alignment mark, exposure and subsequent development are performed, metal plating is performed, and then the resist is peeled off. After washing,
Mass production has been achieved by applying a plate-making plating method for performing post-processing as necessary.

[0007]

The plate-making plating method described in the prior art has the advantage that plating can be performed with high positional accuracy and that plating does not adhere to the side surfaces. However, when a resist film of an electrodeposition photoresist is formed on the surface of a lead frame to be plated in an electrodeposition bath, there is a problem that a uniform coating state cannot be obtained. That is, it is known that the electrodeposited photoresist coagulates and coagulates in an acidic region due to its properties, but the anode side of the electrodeposition bath is "2" when the resist film of the electrodeposited photoresist is formed.
A reaction of “H ₂ O → 4H ⁺ + O ₂ ” takes place and becomes acidic, so that an agglomerated substance of the electrodeposited photoresist is generated. Then, when the coagulated substance of the electrodeposited photoresist is generated as described above, it floats as a foreign substance in the resist tank, adheres to the lead frame, the coating state of the lead frame on the cathode side becomes uneven, the resist remains, Failure modes such as uneven plating and missing plating occur.

The present invention has been made in view of the above problems, and has as its object the purpose of obtaining a uniform coating film of an electrodeposited photoresist and, as a result, applying high quality plating. It is an object of the present invention to provide a plate-making plating method that can perform the plate-making.

[0009]

In order to achieve the above-mentioned object, a plate-making plating method according to the present invention comprises forming a resist film of an electrodeposited photoresist on the entire surface of an object to be plated, pattern exposure and subsequent development. In the plate-making plating method of forming an opening corresponding to a portion to be plated in a resist film and stripping the resist after plating,
It is characterized in that a resist film of an electrodeposited photoresist is formed using an electrodeposition tank in which an anode and a cathode are separated by a partition wall which allows an electrolyte to pass therethrough but does not allow a resist coagulation substance generated on the anode side.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a schematic structural view of an apparatus for performing a plate-making plating method according to the present invention.
An embodiment of the present invention will be described with reference to FIG.

In FIG. 2, reference numeral 10 denotes an electrodeposition tank in which an anode 11 and a cathode 12 are suspended and both are immersed in an electrolyte 13. The cathode 12 is a lead frame as an object to be plated, and is suspended in the electrodeposition bath 10 by a hook 14 so that a resist film of an electrodeposition photoresist is formed on the entire surface of the electrodeposition bath 10. .

In the electrodeposition tank 10, the anode 11 and the cathode 12 are separated by a partition wall 15 made of porous ceramic. The partition wall 15 is configured to allow the passage of the electrolytic solution but not the resist coagulated substance generated on the anode side.

Reference numeral 20 denotes an electrolyte tank, which is arranged to circulate the electrolyte through a pipe between the electrodeposition tank 10 and the electrodeposition tank 10 in order to replace the electrolyte. That is, the electrolytic solution is supplied from the electrolytic solution tank 20 to the electrodeposition tank 10 through the filter 22 by the pump 21, and is circulated by collecting the electrolytic solution from the electrodeposition tank 10.

Further, it is preferable to use aqueous ammonia as a buffer solution in the electrolytic solution used in order to keep the pH constant. The addition of the buffer solution makes it difficult to generate agglomerated substances of the electrodeposited photoresist.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a case where plating is performed on a wire bonding area of a lead frame will be described as an example.

A 0.2 mm thick copper alloy flat plate "EFTEC"
A map type QFN lead frame prepared by etching “64T” was prepared, and the lead frame was pre-processed. Specifically, after removing oil, dirt, and the like attached to the surface of the lead frame using a degreasing solution, the surface was pickled and then chemically polished.

Next, the entire surface of Cu is exposed to Cu in a general cyan bath.
Strike plating was applied to a thickness of 0.3 μm, and a resist film of an electrodeposition photoresist was formed on the entire surface from above. Specifically, an apparatus of the type shown in FIG. 2 in which an anode and a cathode are separated by a porous ceramic partition is used, and “Eagle2100ED (SHIPL) is used as an electrodeposition resist material.
EY) in a solution at 35 ° C. for 80 seconds
A voltage of V was applied for electrodeposition.

During the electrodeposition process, agglomerated substances were generated on the anode side 24 hours after the start, but the agglomerated substances did not pass through the partition walls, and thus no agglomerated substances were present on the cathode side. No abnormality was found in the resist film of the lead frame.

Separately from the above-mentioned electrodeposition process, the same electrodeposition was carried out in a state in which aqueous ammonia was added as a buffer solution to the electrolytic solution, and aggregated substances were generated after 168 hours. In other words, when using an electrolyte containing a buffer solution,
It was confirmed that the timing at which the resist components of the electrodeposited photoresist deteriorated and aggregated was delayed.

After the electrodeposited resist was dried, the entire back surface was first exposed with an ultra-high pressure mercury lamp to eliminate the tackiness of the back side resist. Next, after aligning the photomask with the jig hole of the lead frame,
Pattern exposure was performed on the front side resist. Subsequently, a development step was performed to form an opening of the resist film at the tip of the lead. The developer is “Eagle2005 (SHI
(PLEY)) for 60 seconds in a developer at 40 ° C.

Next, silver plating was applied to the opening at the tip of the lead to a thickness of 3 to 10 μm. This silver plating was performed by sparger plating using a general cyan bath. Thereafter, the electrodeposition resist was peeled off. The stripping solution is “Eagle200
9 (SHIPLEY) "for 30 seconds in a 50 ° C. stripper. Then, after the washing, a discoloration preventing treatment was finally performed, followed by drying.

As a result, there was obtained a lead frame free of any remaining resist, uneven plating, chipped plating, and the like.

A semiconductor element was mounted on the lead frame processed as described above. Specifically, first, an adhesive tape was attached to the entire back surface of the lead frame.
Next, a semiconductor element having a die size of 1.8 mm square was Ag.
The paste was die-bonded and cured at 180 ° C. for 1 hour. Next, after performing wire bonding at 200 ° C. for 1 minute, collective molding was performed using an epoxy resin, followed by curing at 180 ° C. for 5 hours. After this resin mold, the adhesive tape was peeled off, plated with Sn, and diced into individual pieces to obtain a QFN type semiconductor package.

[0024]

According to the plate-making plating method of the present invention, a resist film of an electrodeposited photoresist is formed on the entire surface of an object to be plated, followed by pattern exposure and subsequent development to form openings corresponding to portions to be plated. Part is formed on the resist film,
In the plate-making plating method in which the resist is stripped after plating, the electrodeposition is performed using an electrodeposition tank in which the anode and the cathode are separated by a partition wall that allows the passage of the electrolyte but does not allow the coagulation of the resist generated on the anode side. It is characterized by forming a photoresist resist film, so even if the electrodeposited photoresist coagulates on the anode side, no agglomerate exists on the cathode side due to the partition walls, causing an abnormality in the resist film Because of the absence, it is possible to prevent the occurrence of defects such as remaining resist, uneven plating, and missing chips.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a QFN which is one of semiconductor packages.

FIG. 2 is a schematic configuration diagram of an apparatus for performing a plate-making plating method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead frame 2 Die pad 3 Die bond paste layer 4 Semiconductor element 5 Lead 6 Wire 7 Sealing resin 10 Electrodeposition tank 11 Anode 12 Cathode 13 Electrolyte 14 Hook 15 Partition wall 20 Electrolyte tank 21 Pump 22 Filter

Claims (1)

[Claims] 1. After forming a resist film of an electrodeposited photoresist on the entire surface of an object to be plated, pattern exposure and subsequent development are performed to form openings in the resist film corresponding to portions to be plated. In the plate-making plating method in which the resist is stripped after plating, the electrodeposition is performed using an electrodeposition tank in which the anode and the cathode are separated by a partition wall that allows the passage of the electrolyte but does not allow the coagulation of the resist generated on the anode side. A plate-making plating method comprising forming a resist film of a photoresist.